It's The Water Vapor, Stupid!

A new report in Science underscores what many scientists have been saying for years, it's water vapor, not CO2, that has been driving global temperature changes in recent decades. Stratospheric water vapor concentrations decreased by about 10% after the year 2000, slowing the rate of global surface temperature increase over the past 10 years. It also seems likely that water vapor in the stratosphere increased between 1980 and 2000, causing surface temperatures to warm by an extra 30% during the 1990s. These findings show that stratospheric water vapor represents an important driver of decadal global surface climate change, yet the IPCC crowd continues to focus on CO2.

The new report, “Contributions of Stratospheric Water Vapor to Decadal Changes in the Rate of Global Warming,” by Susan Solomon et al. states that from 2000 to 2009 diminished water vapor levels in the upper atmosphere depressed global warming by about 25% compared to that which would have occurred due only to carbon dioxide and other greenhouse gases. More limited data suggest that stratospheric water vapor probably increased between 1980 and 2000, which would have enhanced the decadal rate of surface warming during the 1990s by about 30% compared to estimates neglecting this change.

The water vapor content of the atmosphere is highly variable, ranging from ~0 to 4%. Approximately 99% is contained in the troposphere but it is also present at higher altitudes. Increased stratospheric water vapor acts to cool the stratosphere but it warms the underlying troposphere. Unsurprisingly, the reverse is true for stratospheric water vapor decreases, the stratosphere warms but temperatures near the Earth's surface cool. Previous studies have suggested that stratospheric water vapor may contribute significantly to climate change, the question is by how much. Limited data are available prior to the mid-1990s, making the identification of systematic changes in atmospheric water vapor difficult. Because of calibration issues and limited spatial coverage the magnitude of the radiative effects are also hard to quantify.

Global mean atmospheric water vapor. Image NASA.

Water vapor gets into the atmosphere from a number of sources. For instance, water vapor is consistently the most common volcanic gas, accounting for more than 60% of total emissions during a surface eruption. But it is water evaporating from the surface of the oceans that provides most of the water vapor in Earth's atmosphere. Tropospheric water vapor increases in close association with warming and this represents a major climate feedback. The condensation of water vapor into liquid or ice creates for clouds, rain, snow, and other forms of precipitation.

Most of the phenomena that we experience as weather is caused by water vapor. Less obviously, the latent heat of vaporization is one of the most important terms in the atmospheric energy budget on both local and global scales. The heat energy absorbed by liquid H2O as it turns into water vapor is later released into the atmosphere whenever condensation occurs. For example, latent heat release in atmospheric convection is directly responsible for powering destructive storms such as tropical cyclones and severe thunderstorms.

The feedback loop caused by evaporation is simulated in global climate models. In sharp contrast, current global models are limited in their representations of key processes that control the distribution and variability of water within the stratosphere. There is deep convection that affects the temperatures at which air enters the stratosphere, which results in drying. According to the research article: “Current global climate models simulate lower stratospheric temperature trends poorly and even up-to-date stratospheric chemistry-climate models do not consistently reproduce tropical tropopause minimum temperatures or recently observed changes in stratospheric water vapor.”

Layers of the atmosphere. Image UCAR.

The tropopause is the boundary between the troposphere, the lowest portion of the atmosphere, and the stratosphere, the second major atmospheric layer. Going upward from the surface, it is the point where air ceases to cool with height. More formally, it is the region of the atmosphere where the lapse rate—the rate at which temperature decreases with height—changes from positive to negative. In the stratosphere the warmer layers are higher up and cooler layers farther down. This is the reverse of the troposphere, which is cooler higher up and warmer farther down. How water vapor gets from the lower atmosphere into the stratosphere has been poorly understood. The Science article goes on to state that, in the real world, the contributions of changes in stratospheric water vapor to global climate change may be a source of unforced decadal variability, or they may be a feedback coupled to climate change.

The research assumed that between 1980 and the 1996–2000 period water vapor had increased uniformly by 1 ppmv at all latitudes and altitudes above the tropopause. A total globally averaged radiative forcing of +0.24 W m–2 was obtained for this assumed 1 ppmv increase. By comparison, the radiative forcing increase due to the growth of carbon dioxide was estimated at about +0.36 W m–2 from 1980–1996. “The comparison of these radiative forcings,” the author's state, “suggests that the decadal changes in stratospheric water vapor have the potential to affect recent climate.”

Observed changes in stratospheric water vapor. Solomon et al./Science.

The authors conclude the paper by saying: “This work highlights the importance of stratospheric water vapor for decadal rates of warming based directly upon observations, illuminating the need for further observations and a closer examination of the representation of stratospheric water vapor changes in climate models aimed at interpreting decadal changes and for future projections.” In other words, we need to improve our theoretical knowledge, gather better data, and make more changes to those inaccurate climate models.

Once again our limited understanding of the mechanisms that control Earth's climate is revealed. Here is a plausible explanation as to why the period from 1980 to 1999 was one of noticeable warming, and why since 2000 things have leveled off or even cooled down a bit. Because the mechanisms that link water vapor to temperature regulation are complex and not well understood the climate change clique concentrated on CO2—and it has become obvious that treating CO2 as a form of planetary thermostat is simply not a viable explanation. It is no wonder that the IPCC's carbon dioxide centric climate models didn't get recent temperature swings right. To steal a phrase from American politics, “It's the water vapor, stupid!”

Be safe, enjoy the interglacial and stay skeptical.

water vapor in high stratosphere

thanks, great analysis.

Finally... Scientific evidence consistent with AGW skepticism

You will have greater credibility as a "skeptic" if you provide a factual representation of the science.
This study speculates that 30% of warming during the 1990s may have been due to increasing water vapor content of the stratosphere, not 100% of the warming from the 1980s & 90s, as you've indicated. That still leaves quite a bit of warming unaccounted for. It may be your conclusion that CO2 was not responsible, but the paper surely doesn't say that.
You indicate that the "IPCC crowd" (whoever they are) have no interest in considering water vapor as a driver, yet this paper was written by the co-chair of Working Group I (AR4).
The important implication of this paper is that a respected group of climate scientists are saying that pre-2000 warming was not entirely due to AGHGs. The source of the water vapor is uncertain, but at least there's some debate about it. I have the feeling you don't quite "get it". At long last AGW skeptics have scientifically defensible evidence to support their position.

Where do you get 100% from?

Where in the article did I say that stratospheric water vapor was responsible for 100% of atmospheric warming? Perhaps you should read the article before commenting on it. The unvoiced part of this news is the fact that CO2 mongering climate change extremists, knowing that carbon dioxide can not create the observed amount of temperature increase on its own, cite as their primary explanation a positive feedback effect between CO2 and water vapor. This report shows that water vapor's influence does not follow the monotonically increasing CO2 curve and can even act counter to it. Add in changes in insolation, which have been found to be three times more potent than previously accepted, the effects of aerosols, and NOx and there is practically no room for any CO2 induced warming. Do you "get it" now?


"It is no wonder that the IPCC's carbon dioxide centric climate models didn't get recent temperature swings right."

It is no wonder that the IPCC is being dismantled daily. Apparently, they were caught citing Greenpeace for a second time!

Environmentalism causing increased water vapor.

Is this just another example of where do-gooder Environmentalism has aggravated the problem?

Since the 70's every time a new power plant has been built it has had cooling towers rather than dumping the latent heat into rivers and lakes. Could these cooling towers be aggravating the problem? Power plants are no better than 50% efficient, that means that the same amount of power being delivered to the customer is being dumped into the environment. But with cooling towers we are taking the latent heat of vaporization and causing water vapor, with this heat, to be dumped into the atmosphere and making a cloud for each power plant. The number if industrial coolers, the ones on the top of large buildings for air-conditioning, has also increased over the last 40 years. Essentially every large building now has an industrial cooler for the air-conditioning system. Even in the winter months these coolers are operating to remove all of the heat trapped inside these buildings (from people, computers, equipment, etc.) and dumping more water vapor into the atmosphere. Most large buildings now have NO heating facility - just cooling equipment. And, water vapor is much lighter (H2O) than carbon-dioxide (CO2), quite a bit lighter. Boil water, where does the steam/water vapor go? Release a CO2 fire extinguisher, where does the CO2 vapor go?

Water vapor from power generation

Interesting conjecture. According to a PNAS report by B, D. Santer et al. the recent increase in water vapor is primarily due to human-caused increases in GHGs and not to solar forcing or volcanic eruptions. Satellites have observed an increase in atmospheric water vapor of about 0.41 kg/m2 per decade since 1988. Observations show the increase in water vapor is around 6 to 7.5% per degree Celsius warming of the lower atmosphere. The observed changes in temperature, moisture, and atmospheric circulation fit together in an internally and physically consistent way. Then again, they attributed all water vapor from evaporation due to global temperature rise as human caused—direct emissions are another story.

The US EPA's 2009 report on the Atmospheric Concentrations of Greenhouse Gases states, “water vapor is not tracked in this indicator, as it is generally accepted that human activities have not increased the concentration of water vapor in the atmosphere.” But according to EPA Director of the Department of Pollutant Decrees, Ray Donaldson: “Back before carbon dioxide was dangerous, we simply assumed that water vapor was also benign. But all reputable scientists now agree that the increased water vapor content of the atmosphere from such sources as burning of fuels and power plant cooling towers will also enhance the greenhouse effect, leading to potentially catastrophic warming.” Of course the EPA finds pollutants in every human activity. Thank goodness Mr. Donaldson added, “right now, we are not so concerned about the water vapor exhaled by people. That is low on our list of priorities.”

When you think about the amount of energy released in a typical tropical storm, all of which comes from water vapor condensing back into liquid or solid H2O, it seems improbable that direct human water vapor emissions from cooling towers could have much of an impact on climate. To put this in perspective, a DOE whitepaper, “Water Vapor from Thermoelectric Power Plants,Does it Impact Climate?,” found that the total amount of water released from processing and burning all the world's fossil fuel reserves at once would yield about 1 x 1016kg of water vapor. Spreading the effect of the conversion over 100 years gives a water vapor emissions rate of 1 x 1014kg water vapor per year. The current amount of water vapor in the atmosphere is 1.3 x 1016kg water. By this estimation, human emissions from power generation is less than 1% of the total amount of water vapor in the atmosphere or 0.02% of annual rainfall worldwide (5 x 1017kg water).

Wish our cooling towers were that efficient.

Check ->

"Most nuclear power (and other thermal) plants with recirculating cooling are cooled by water in a condenser circuit with the hot water then going to a cooling tower. This may employ either natural draft (chimney effect) or mechanical draft using large fans (enabling a lower profile but using power). The cooling in the tower is by transferring the water's heat to the air, both directly and through evaporation of some of the water. In the UK the water requirement for a 1600 MWe nuclear unit is about 2 cubic metres per second (173 ML/d), this being about half for evaporation and half for blow-down (see below)."

Even Wikipedia gives better info on how wasteful Industrial coolers and cooling towers are.

"Cooling towers for chillers often are the largest consumers of water in buildings. Because these systems rely on water evaporation as part of the air conditioning process, they churn through thousands of gallons of water every minute. Considering that the average cooling tower uses three gallons of water per minute for every ton of cooling, a large commercial building with 1,000 tons of refrigeration will use 3,000 gallons of water per minute—10 times the amount of water used in the average household each day.² "

The price of innumeracy

I don't think you understand the magnitude of the yearly water vapor number given above. 1 x 1014 is 100 billion metric tons of H2O, about six times the amount of CO2 emitted per year. The important point is that, because water vapor is a much more plentiful component of the atmosphere and also because water vapor does not stay in the atmosphere very long (think precipitation), the seemingly huge amount of human created water vapor is just a drop in the bucket.

As for comparing the water vapor from an industrial cooling tower with the emissions from a home, a single power plant could service a million homes. Estimates for cooling water vapor emissions come in at around 25 gigatons, boosting the human “industrial activity” total to 125 gigatons, still under 1% and still just a drop in the bucket. If you want to find the largest source of water vapor directly attributable to humans I would look to crop irrigation, which uses 70% of the freshwater consumed world wide. Your title, implying that there was something wrong or misleading with my estimation, is either naive or disingenuous.

No disrepect intended.

I am a retired Nuclear power plant employee, and was implying that the cooling towers at the plant I worked at dumped an awful lot of water into the air, and that these numbers did not seem to provide a good estimation of the amount of water they evaporate. I do not remember the exact capacity of the cooling tower make-up pumps (I was an instrumentation engineer, not mechanical) however, I do remember that the makeup flow was greater than that of a typical fire hydrant. The supply pipe was at least 8 inches in diameter. When you shut down a make-up pump you could see the water level decrease. The evaporation was so high that about half of the make-up flow was used just to flush out the accumulation of salts of evaporation and contamination collected from the air (as I was told in my training classes.) The make-up rate was about 10% of the recirculation rate (again, as I was told in my training classes.) At times two of the three pumps were running. The reference to emissions from a home was not about homes, but, just to show how much a typical air-conditioning industrial cooler ALSO adds water to the atmosphere. When traveling by air I have seen the man-made clouds drifting downwind of cooling towers around power plants for more than a mile and clearly recall seeing one down-wind of the industrial cooler for the local mall. The clouds are often visible at Salem/Hope Creek as you fly into WashDC or Baltimore. These clouds must do something to the local temperature. Some people even claim that there is even higher snowfall downwind of cooling towers. All of that water put into the atmosphere also contains the latent heat of evaporation, which must also do something to the atmosphere. With lake/ocean evaporation, the suns heat is evaporating the water, which I see as a net-zero gain/loss. However, a 1,000 MWe power plant is actually (about) 3,000 MWt (t = thermal). That means that (about) 2,000 Mw of energy are being dumped into the atmosphere. It must do something! I would assume that these hot little H20 molecules (that are lighter than O2) would have more of an effect than cold CO2 molecules that sink to the ground.

Sorry if I was a bit grouchy

If I was a bit grouchy on my last reply it is because I have been wrestling with some form of flu bug for the past several days and in a foul mood. As you say, cooling towers can and do pump a lot of water vapor into the lower atmosphere and can indeed influence local weather. The point that I was trying to communicate was that, as large as the amount of H2O vaporized by a nuclear power plant is, it is still down in the white noise when it comes to the entire hydrological cycle. There is no doubt that human activity influences Earth's environment in a number of ways.

As I mentioned, irrigation is probably has the biggest impact on atmospheric moisture. The evaporation of irrigation water has been estimated to cause a globally averaged surface cooling of 0.15 Wm–2. The surface cooling rate can be as large as 30 Wm–2 in highly irrigated areas. Of course this means that somewhere else within the atmosphere all that latent heat will get released when the water vapor turns into precipitation.

How much power generation heats the planet is another matter. Most of the energy we expend originally arrived as radiation from the Sun, nuclear energy excepted. I'll have to do some calculations when my head is clearer, but I suspect that it isn't all that noticeable either. After all, life and the environment are just byproducts of solar energy trying to escape back into space.

cooling towers

I think the issue with cooling towers and irrigation is cloud formation, like jet contrails.

To my limited knowledge (please correct me), clouds reflect more during the day than they trap; but trap heat at night, causing a tightening of day and nighttime temperatures. Perhaps the overall result is cooling. But it also brings in some small percent of added water vapor, with infrared absorbing effect, adding to heat.

I guess the effect is minor cooling?

(I think the heat lost from burning fuels is already taken into account and is about 2 orders of magnitude smaller than the apparent heating effect.)

I think we are saying the same thing

That's what I was alluding to when I mentioned the cooling from irrigation evaporation. The heat doesn't disappear, it just gets moved to somewhere else in the troposphere. The other poster's speculation about water vapor from power plants is another story. The latent heat from that source would be additional energy to the climate, even if it is comparatively small, and could raise the RH however slightly.

Sorry, I meant saturation vapor preasure

I misspoke. I meant to say saturation vapor pressure, which increases exponentially with temperature, not relative humidity.

Let us if Dr. Pachuri and Al

Let us if Dr. Pachuri and Al Gore demand ban on watering golf courses, if not on our bathing!!

M I Bhat


Maybe they should have taxed water as well as CO2 - oops just realised they are doing both!